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332

Corrugated Flues.

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through to the end k^ thence by brickwork flues, along the bottom
of the boiler to the front, again to the back end by the brick side
flues, and away to the chimney. The internal flues are therefore
at a greater heat than the rest of the boiler; this, producing
expansion, necessitates the introduction of elastic portions. The
flues, moreover, are in danger from collapse, for a cylinder,
although strong when pressed from within, is unstable when
pressed from without; so strengthening rings are applied at various
distances along the circumference. But as joints have to be
formed, on account of the great length of the flues, it is customary
to make provision for elasticity lengthwise, and rigidity of cross
section also, at these places, the most usual method being by the
introduction of the Adamson flanged seam at e. This joint .has
the advantage over other methods, of shielding the rivet heads from
flame, and a slightly projecting annular strip is placed between the
flanges for caulking purposes. The space between the tubes
being small, the seams are made to ' break joint' longitudinally,
so as to be easily got at when necessary. Conical ' Galloway'
water tubes are sometimes inserted, as at D, for intercepting the
heat more satisfactorily, the smaller end being passed in at the
larger hole. The flues are joined to the end plates by angle
rings, and their diameters decrease at k^ the connection being
formed by the conical portion /. The manhole edge at f is
strengthened by a riveted ring, always added when a large hole
is removed; and the mudhole n is similarly treated, a portion of
plate being left all round, on which to place the internal door.
Holes are cut for various fittings, as at #, g, and h. The circular
seams are single riveted, but double riveting is used for the
longitudinal joints, because any boiler receives but half the stress
longitudinally that it does in a circumferential direction (seep. 398).

Fox's corrugated flues, shewn In section at E, are extensively
used for the furnaces of many boilers, taking the place of the two
pieces //; while f is equivalent to the portion k. The corruga-
tions give not only strength and elasticity, but a larger heating
surface.

The proportion of length to breadth in the boiler shewn is the
largest allowed; more often the length is about two-thirds of that
(See Appendix 11^ p. 827.)